Conventionally, magnetic field generators in which an orientation of a magnetic field at a target position is variable are public. The applicant of the present invention proposed one in Patent Document 1. According to the magnetic field generator disclosed in Patent Document 1, a magnetic field generating unit of a large diameter and a magnetic field generating unit of a small diameter housed therein are rotated circumferentially, whereby the orientation of a magnetic field which is provided at a target position within the small-diameter magnetic field generating unit is varied on a radial plane.
Meanwhile, in recent years, there have been developments in the field of medical care for medical instrument systems which guide, by working of a magnetic field, an object such as a catheter and a capsule endoscope to an arbitrary position inside the body of a patient. In order to guide an object to an arbitrary position, it is necessary to be able to vary the orientation of the magnetic field at the target position in all directions (any direction). Therefore, the magnetic field generator according to Patent Document 1 which varies the orientation of the magnetic field on a predetermined plane is not applicable to such medical systems. For this reason, these medical systems make use of magnetic field generators such as one disclosed in Patent Document 2 for example. The magnetic field generator disclosed in Patent Document 2 is capable of varying the orientation of the magnetic field at a target position in all directions by circumferential rotation of one magnetic field generating unit and radial travel of the same one magnetic field generating unit.    Patent Document 1: JP-A Hei 9-90009    Patent Document 2: JP-A 2002-536037